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Observations of the line-of-sight component of emitter velocities in galaxies are valuable for reconstructing their 2D velocity fields, albeit requiring certain assumptions. A common one is that radial flows can be neglected in the outer…
The recent findings of Romanowsky et al., of an ``unexpectedly'' small mass discrepancy within 5 effective radii in several elliptical galaxies, are not surprising in the context of MOND. As we show here, they are, in fact, in full…
We briefly describe our on-going investigation of the near-IR luminosity-metallicity relationship for dwarf irregular galaxies in nearby groups of galaxies. The motivations of the project and the observational databases are introduced, and…
The metal-poor gas continuously accreting onto the discs of spiral galaxies is unlikely to arrive from the intergalactic medium (IGM) with exactly the same rotation velocity as the galaxy itself and even a small angular momentum mismatch…
Observations consistently show that elliptical galaxies follow a tight "fundamental plane" scaling relation between size, mean surface brightness and velocity dispersion, with the form $R \propto \sigma^{a}\mu^{b}$. This relation not only…
This thesis presents observational studies of evolution of dwarf elliptical galaxies. dE's are numerically dominant population in clusters of galaxies, but their origin and evolution is a matter of debate. Several scenarios of gas removal…
The acceleration of the expansion of the universe arises from unknown physical processes involving either new fields in high energy physics or modifications of gravitation theory. It is crucial for our understanding to characterize the…
The dynamical and virial mass of the Milky Way galaxy is estimated using latest high precision stellar halo and dwarf galaxy satellite kinematics. The new data suggest the Galaxy is a highly compact, classically thermalized object.…
Galactic rotation curves exhibit diverse behavior in the inner regions, while obeying an organizing principle, i.e., they can be approximately described by a radial acceleration relation or the Modified Newtonian Dynamics phenomenology. We…
The stellar velocity dispersion, $\sigma$, is a quantity of crucial importance for spiral galaxies, where it enters fundamental dynamical processes such as gravitational instability and disc heating. Here we analyse a sample of 34 nearby…
The observed number of dwarf galaxies as a function of rotation velocity is significantly smaller than predicted by the standard model of cosmology. This discrepancy cannot be simply solved by assuming strong baryonic feedback processes,…
The physical processes defining the dynamics of disk galaxies are still poorly understood. Hundreds of articles have appeared in the literature over the last decades without arriving at an understanding within a consistent gravitational…
Hubble Space Telescope Advanced Cameras for Surveys has been used to determine accurate distances for 20 galaxies from measurements of the luminosity of the brightest red giant branch stars. Five associations of dwarf galaxies that had…
I consider in light of MOND the three debris galaxies discussed recently by Bournaud et al.. These exhibit mass discrepancies of a factor of a few within several scale lengths of the visible galaxy, which, arguably, flies in the face of the…
We report on the recent developments of our long-term investigation of the near-IR luminosity-metallicity relation for dwarf irregular galaxies in nearby groups. A very well-defined relation is emerging from our observational database, and…
The discrepancy between the visible mass in galaxies or galaxy clusters, and that inferred from their dynamics is well known. The prevailing solution to this problem is dark matter. Here we show that a different approach, one that conforms…
A conservative scaling model based on Newton's law of circular motion and the virial theorem is proposed. Employing dimensionless scaling relations, a physical solution to the Baryonic Tully-Fisher Relation (BTFR) is obtained and the origin…
The mass-radius relation of white dwarfs is largely determined by the equation of state of degenerate electrons, which causes the stellar radius to decrease as mass increases. Here we observationally measure this relation using the…
We have performed a large observing campaign of intermediate-redshift disk galaxies including spectroscopy with the FORS instruments of the VLT and imaging with the Advanced Camera for Surveys onboard the HST. Our data set comprises 113…
As an alternative to dark matter models we use generalized Jordan-Brans-Dicke scalar-vector-tensor (JBD-SVT) gravity model to study the behavior of the rotational velocities of test particles moving around galaxies. To do so we consider an…